A heating system coupled to an engine utilizes an engine-driven pump to circulate coolant and transfer engine heat to a heater core for heating a vehicle passenger compartment. In some vehicles, such as hybrid-electric vehicles and diesel engine vehicles, the amount of waste heat generated by the engine may not be sufficient to rapidly heat the vehicle cabin.
One example approach for selectively increasing engine heating is illustrated by Tanaka et al. in U.S. Pat. No. 6,695,743. Therein, the engagement of a torque converter lock-up clutch is adjusted based on the vehicle speed and based on a heating requirement. Specifically, when the vehicle is moving and a higher amount of heating is requested, the engagement of the lock-up clutch is restricted (or restricted more) while when a lower amount of heating is requested, the engagement of the lock-up clutch is unrestricted (or restricted less). In this way, the engine may generate increased waste heat via inefficiencies created by a disengaged torque converter.
However, the inventors herein have recognized potential issues with such an approach. As one example, if the vehicle is idling, no additional engine waste heat can be generated according to this approach. Thus, if the vehicle has an extended idle, the cabin occupants may not be provided desired cabin heat for a significant duration, which may decrease customer satisfaction.
Thus, in one example, some of the above mentioned issues may be addressed by a method of operating a vehicle engine coupled to a transmission, comprising during a vehicle stopped condition, grounding the transmission to a frame of the vehicle. The method further comprises, increasing engine output with the transmission grounded to generate increased waste engine heat. The generated waste heat may then be used to heat the vehicle cabin.
In one example, during a vehicle stopped condition, for example, when a gear shift indicator is in park or neutral vehicle, and the engine is idling, an engine controller may be configured to lock the transmission output by grounding the transmission to a frame of the vehicle with the torque converter unlocked (for example, at least partially unlocked). Further, the engine output may be temporarily increased, by increasing a fuel injection and/or aircharge intake, to increase engine idle speed. The transmission may be grounded and the engine input may be increased in response to a cabin temperature falling below or a threshold, or in response to a vehicle occupant requesting cabin heating. The transmission may be grounded by engaging one or more transmission output shaft to transmission case clutches. By engaging such a clutch while the torque converter is unlocked, the output of the transmission may be ground to a vehicle frame, thereby transmitting substantially no torque through the transmission. At the same time, by increasing the engine output to increase an engine idle speed, the torque converter may be rotated in coordination with the higher engine idle speed, thereby generating additional waste heat. As such, during such an operation, the amount of waste heat generated through the torque converter may be directly proportional to the cube of engine idle speed. Thus, a large amount of heat may be rapidly generated by raising the engine speed input to the torque converter while transmitting substantially no torque from the transmission.
The large amount of waste heat generated in this manner may then be used for rapid cabin heating. For example, coolant may be circulated through the engine during the transmission grounding with increased engine input operation. The heated coolant may then be circulated through a vehicle cabin heating system to heat the vehicle passenger compartment. In an alternate example, transmission fluid may be circulated through the engine during the operation and the heated transmission fluid may be circulated through a heat exchanger of the vehicle cabin heating system. Additionally or optionally, the generated waste heat may be used for cold-start emission control device catalyst heating, cold-start transmission heating, or combustion stabilization during CSER. As such, if no heating is requested, the transmission and torque converter lock-up clutch may be disengaged until a vehicle re-launch is requested.
In this way, during vehicle idling conditions, a transmission output may be locked while an engine input may be increased to generate additional waste engine heat. By increasing the engine idle speed with the transmission grounded while a torque converter coupled between the engine and the transmission is unlocked, substantial amounts of waste heat may be rapidly generated. By exchanging the waste heat with a coolant of the vehicle's cabin heating system, cabin heating may be enabled even during vehicle stopped and engine idling conditions. By using existing vehicle components to provide the requested heating, the operation of auxiliary heat-producing devices may be reduced.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.